CB to 10 (MHz)

At this time in the current sunspot cycle it seems that by the time I get home the upper bands are quiet. Forty is hopping, but very crowded and noisy. "Thirty"--10 MHz--has space, no phone QRM, and with a power limit of only 200 watts, a more level playing field. -- So what for an antenna?

All the useful dipole supports near the shack were already in use, so a vertical was a logical choice--let's see, 234/10.1=about 23'5" or so--uh oh, no pole that tall on hand. An old edition of the Handbook details the "helically wound vertical" that can use a much shorter support pole. Hey, that old CB "Big Stick" fiberglass form looked just about right. It had a sturdy 12' lower section, all fiberglass (I'm sure it's similar to a lot of different brands of CB "half wave" verticals that a lot of us have kicking around). The book states that a half-wave of wire, wound evenly as a helix, will fall just short of an equivalent quarter-wave vertical.

After winding 46' from top to bottom, hooking a few 23' radials to the coax shield, and testing for SWR it was found to be a bit short. No real problem, I spliced a couple more feet of (insulated, #16 speaker) wire to the end and tried again. After a few tries the SWR was 2:1. I should have been content with that, but I am a bit of a purist and tried shortening and lengthening the wire, but 2:1 seemed to be the lower limit, perhaps it was already "resonant" but the resulting impedance was something other than 50 ohms, likely closer to 25? What finally succeeded was an old trick I read about somewhere, of using an old piece of coax as a capacitor. I soldered the center wire of a 4' length of RG-58 to the antenna and the braid to the radial connection, and tried again. This worked, and at about 30" of coax the SWR was now 1.5:1--good enough to get the full power out of my IC-718. Every installation will be different, of course, but this technique may be useful if you run into that situation.

Performance? It's no beam, but I get reports similar to those I give, which isn't bad for six watts output. Perhaps a dipole 46' up would be more efficient, but below that the radiation angle would be high and most DX comes in at a low angle. Oddly enough, this antenna seems quieter than my 40 Meter Inv. L, but this could be due to the higher frequency.

If you need a quick antenna for this band try the helix--I'll be happy to correspond with anyone wanting more info. 73, GL..._._

P.S. The reference to "CB" in the title was just a ruse to get your attention-did it work? Actually, no reason you couldn't use a pole-vaulting pole or a sturdy bamboo if well lacquered and taped. Even PVC would probably be OK, but the thin stuff is too weak and the thick stuff too heavy. Raw wood would likely saturate after a rain, but almost any good dielectric should do the job. I haven't tried an old plastic garden hose, but that would probably work too, supported internally by a nylon rope. Perhaps there should be a prize for the most imaginative support pole?

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